System and method for fast weighing of items such as mailpieces

ABSTRACT

A system and method for fast weighing of items such as mailpieces. The system includes a scale system having a platform connected to a load cell that provides an output signal to an analog-to-digital converter. The resulting digital output signal is processed by a low pass filter and analyzed by a microprocessor to determine weights of items on the platform. The microprocessor also determines postage amounts of items on the platform. The microprocessor also determines postage amounts as functions of the weights and outputs these postage amounts to a postage meter. The microprocessor determines the weights as the median of the peak to valley difference of the digital output signal when the digital output signal peak to valley difference is less than a predetermined value. The microprocessor identifies peaks and valleys of the digital output signal by determining when the derivative of the signal changes sign. The microprocessor uses the determined first peak value to determine if the weight is below the first weight break point. The microprocessor also estimates the weight as an average of a sum of medians for N preceding cycles if the digital output signal does not converge. The postage meter initially assumes that all mailpieces have a minimum postage amount due and corrects the postage amount when a weight signal is received from the microprocessor so as to take advantage of the fact that the majority of mailpieces require only a minimum postage amount.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a system and method for rapidweighing of items. More particularly it relates to scale systems used inpostage metering systems to weigh, and determine postage for, mailpiecesor the like.

[0002] Postal scale systems are well known. Such scale systems weigh amailpiece and determine the appropriate postage for that mailpiece as afunction of the weight. Postal mailing systems where a mailpiece istransported onto a postage scale system, the appropriate postage isdetermined, and the mailpiece is then transported to postage meteringsystem for imprinting with a postal indicium representative of thepostage determined are also known. One such system is described in U.S.Pat. No. 4,742,878; issued May 10, 1988. In such systems there is aconstant need to increase the rate at which the scale can determine theweight of a mailpiece in order that the throughput of the system can beincreased.

[0003] U.S. Pat. No. 4,787,048; issued: Nov. 22, 1988, discloses oneapproach to decreasing the time required for a postage scale system todetermine the weight of a mailpiece. The system disclosed in this patenttakes advantage of the structure of postage rate charts, i.e., thefunction that relates the weight of the mailpiece to the appropriatepostage amount. Such rate charts provide a constant postage value forall weights between a pair of predetermined weight breaks. The system ofthe '048 patent takes advantage of this by use of an algorithm where afirst estimate of the weight is made and used to determine the postageamount unless the first estimate is within a predetermined distance of abreak point, in which case a second more accurate estimate is made.

[0004] A basic cause of the delay in determining weight for a mail pieceis the tendency for a scale system to oscillate in response to thearrival of the mailpiece on the system. These oscillations are damped,but only slowly arrive at a new stable output value representative ofthe weight of the mail piece. Heretofore systems have relied on anaveraging process over a number of samples taken over a number of cyclesof the oscillations to approximate the weight output. While systemsusing such averaging type algorithms have generally proved satisfactoryin the past, presently they are approaching limits such that it isdifficult to increase the throughput of postage metering systems usingsuch algorithms. This problem can be exacerbated by the presence ofexternal vibrations, which can slow or even prevent the scale systemoutput from converging to a sufficiently accurate approximation of theweight.

[0005] Thus it is the object of the present invention to provide a scalesystem, and a postage metering system incorporating such scale system,which can more rapidly determine the weight of a mailpiece or the like.

BRIEF SUMMARY OF THE INVENTION

[0006] The above object is achieved and the disadvantages of the priorart are overcome in accordance with the subject invention by a methodand system for determining a weight for an item, where a scale systemgenerates a digital output signal. The scale system includes: a supportfor supporting the item; a transducer for generating the digital outputsignal, the signal being representative of an instantaneous response ofthe support; a data processing system for, in response to the digitaloutput signal, detecting presence of the item on the support; and thendetermining if a next peak to valley difference in the digital outputsignal is less then a predetermined value; and, if so, determining theweight to be equal to a median of the difference and exiting; andotherwise returning to determine a next peak to valley difference insequence.

[0007] In accordance with another aspect of the present invention, thepeaks are identified by determining when a first derivative of thedigital output signal changes from positive to negative, and the valleysare identified by determining when the first derivative changes fromnegative to positive.

[0008] In accordance with another aspect of the present invention, theweight is determined only if the median is less than one-half of animmediately previous median.

[0009] In accordance with still another aspect of the present invention,the data processing system returns to determine if a next peak to valleydifference only for a predetermined number of times; and then determinesthe weight to be an average of the predetermined number, or a lessersufficient number, of previous medians.

[0010] In accordance with still another aspect of the present inventionweights are determined with at least sufficient accuracy to assure thatthe weight is within one of a plurality of ranges, the ranges beingbounded by break weights, the scale system is critically damped oroverdamped, and the data processing system responds to the digitaloutput signal detecting presence of the item on the support to determineif a first peak in the digital output signal is less than a lowest ofthe break weights and, if so, determines the weight to be in a lowest ofthe ranges; and otherwise determines if a next peak to valley differencein the digital output signal is less then a predetermined value; and, ifso determines the weight to be equal to a median of the difference andexits; and otherwise returns to determine if a next peak to valleydifference in sequence is less then the predetermined value.

[0011] In accordance with another aspect of the present invention, thepredetermined value is a predetermined fraction of the smallest of theranges.

[0012] In accordance with still another aspect of the present invention,the items are mailpieces and postage for the mailpieces is determined bythe ranges.

[0013] In accordance with still another aspect of the present invention,the system includes a postage metering system responsive to the dataprocessing system for franking the mailpieces, and the postage meterresponds to detection of the mailpiece to debit a vault for a minimumpostage amount corresponding to the lowest range and then later debitsthe vault for an additional postage amount only if the first peak isgreater than the lowest break weight.

[0014] Other objects and advantages of the subject invention will beapparent to those skilled in the art from consideration of the detaileddescription set forth below and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 shows a schematic block diagram of a postage meteringsystem including a scale system.

[0016]FIG. 2 shows a graphic representation of the response of the scalesystem of FIG. 1 to a mailpiece.

[0017]FIGS. 3A and 3B show a flow diagram of processing of the responseof FIG. 2 by the scale system of FIG. 1 to determine the weight of amailpiece.

[0018]FIG. 4 shows a graphic representation of the response of the scalesystem of FIG. 1 to a mailpiece in the presence of external vibrations.

[0019]FIG. 5 shows a flow diagram of processing of the response of FIG.4 by the scale system of FIG. 1 to determine the weight of a mailpiece.

[0020]FIG. 6 shows a flow diagram of postage accounting for a mailpieceweighing less than 1 ounce by the postage metering system of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0021] In FIG. 1 postage metering system 10 includes scale system 12 andpostage meter 16. Postage meter 16 includes vault 17 (i.e. secureaccounting registers) and is programmed in accordance with the presentinvention to quickly account for mailpieces requiring only minimumpostage. Scale system 12 includes load cell 20, producing a response(shown in FIGS. 2 and 4) to the force from platform 22; analog-todigital converter 24, for converting the output of load cell 20 to asequence of digital values; low pass filter 28; and microprocessor 34,for processing a filtered output to determine a weight and provide anoutput representative of the postage corresponding to that weight topostage meter 16. In accordance with the present inventionmicroprocessor 30 is programmed with a novel algorithm for rapididentification of mailpieces that are less than a predetermined firstbreak weight, which require only minimum postage, and for rapidestimation of a weight for mailpieces that exceed the first breakweight. (While filter 28 is shown as a separate element in FIG. 1 forsimplicity of illustration, it should be noted that filter 28 can be,and preferably is, implemented by software running in microprocessor30.)

[0022] In the embodiment shown in FIG. 1 load cell 20, converter 24, andfilter 28 form a transducer for generating a digital output signalrepresentative of the response of scale system 12. Other embodiments,where other types of transducers generate the representative signal, arealso within the contemplation of the present invention.

[0023]FIG. 2 shows the response of scale system 12 when a mailpiecearrives on platform 22, i.e., the displacement of platform 22 and thecorresponding analog signal S(t) produced by load cell 20. Signal S(t)can be modeled as a damped sinusoid, which varies about a level Wrepresentative of the weight of the mailpiece. Prior to time t0 signalS(t) varies about a 0 tare level representative of the weight ofplatform 22 without any additional load, and at time t0 rises to firstpeak P1. Since scale system 12 will be critically damped, or overdamped,peak P1 will be the maximum value of signal S(t); and, if peak P1 doesnot exceed first break weight B, it can be assumed that the weight ofthe mailpiece is in a lowest range and the mailpiece will requireminimum postage, as will be discussed further below. If P1 exceeds breakweight B then, in accordance with the present invention, scale system 12estimates the weight of the mailpiece by considering the differencebetween successive peaks and valleys; P2-V2, P3-V2, P3-V3, . . . Whenthis difference is less than a predetermined amount for a peak, valleypair, Px, Vy, then scale system 12 estimates the weight as the median ofthat peak, valley pair, M(Px, Vy). Preferably the predetermined value isa fraction, preferably {fraction (1/10)}, of the minimum range for agiven postal rate, typically one ounce, and the first break weight isone ounce.

[0024]FIGS. 3A and 3B show a flow diagram for the operation of themicroprocessor 30 in carrying out the algorithm described above withrespect to FIG. 2. At step 40 microprocessor 30 tests determine ifsignal S is greater than the 0 tare and, if not, continues to loopthrough step 40. (Note that signal S is a sequence of digital valuescorresponding to samples of signal S(t).) Preferably these signals aretaken at one or two milliseconds intervals, which is approximately anorder of magnitude less than the sample interval for previous scalesystems, so that dS/dt can be satisfactorily approximated as thedifference between successive sample values of signal S(t).

[0025] Once signal S is determined to be greater than 0 then, at step42, microprocessor 30 determines if dS/dt is greater than 0 for 3successive sample intervals. By requiring that dS/dt be greater than 0for 3 intervals, small high frequency perturbations are filtered out.Microprocessor 30 remains at step 42 until the condition is satisfiedand then goes to step 44 to test if dS/dt is less than 0 for 3successive sample intervals. Again, microprocessor 30 remains at step 44until the condition is satisfied. Then at step 46 the peak is determinedas the first value in the sequence of values identified at step 44, orin any other convenient manner.

[0026] Then at step 50 microprocessor 30 determines if the peakidentified at step 46 is greater than the first break weight, which forthe U.S. Postal Service is typically one ounce, and, if not, at step 52calls and validates the weight as being less than one ounce, and exits.(Calling a weight, as used herein, means microprocessor 30 uses thecurrent weight value to determine the postage for a mailpiece.Validating a weight, as used herein, means that microprocessor 30calculates the net weight and insures that it is above 0 and withinmaximum scale limits.)

[0027] If the peak is greater than the first break weight B, then atsteps 54 and 58, microprocessor 30 again searches for three successiveintervals where dS/dt is greater than 0 followed by three intervalswhere dS/dt is less than 0 to identify a second peak in signal S. Oncethe conditions at steps 54 and 58 are satisfied then at step 60microprocessor 30 determines and saves the second peak.

[0028] Then at step 62 microprocessor 30 again searches for threesuccessive intervals where dS/dt is greater than 0 to identify the nextvalley in signal S. Then at step 68 microprocessor 30 computes thedifference between the peak value, saved at step 60, and the currentvalley value, determined at step 66.

[0029] At step 70 microprocessor 30 determines if this difference isless than a predetermined fraction of a minimum range, preferably lessthan 0.1 ounce and, if so, at step 74 determines if this difference isgreater than ½ of the difference between the previous peak and valleypair. The test at step 74, and the same test at other steps describedbelow, form a second filter to assure that high frequency perturbationsdo not cause a false determination of a peak or valley. If bothconditions at step 70 and step 74 are satisfied, then at step 76microprocessor 30 calls and validates the weight as the median of thedifference computed at step 68 and then exits. Otherwise microprocessor30 goes to step 80 (shown in FIG. 3B).

[0030] At step 80 microprocessor 30 again tests to find 3 successiveintervals where dS/dt is less than 0 to identify the next peak, and atstep 82 determines and saves the next peak when found. At step 84microprocessor 30 computes the difference between the current peak,determined at step 82, and the valley, saved at step 66.

[0031] Then at step 86 microprocessor 30 again determines if the peak tovalley difference is less than {fraction (1/10)} of an ounce, and atstep 90 if the difference is greater than ½ of the previous peak tovalley distance. If both conditions are satisfied then at step 92microprocessor 30 calls and validates the weight as the median of thepeak to valley difference determined at step 84 and exits.

[0032] Otherwise, at step 94 microprocessor 30 again searches for threesuccessive intervals where dS/dt is greater than 0 to identify the nextvalley. Once 3 such intervals are found then, at step 98, microprocessor30 determines and saves the valley. Then at step 100 microprocessor 30computes the peak, saved at step 82, minus the current valley,determined at step 98.

[0033] Then at steps 102 and 106 microprocessor 30 again tests todetermine if the difference computed at step 100 is less than {fraction(1/10)} ounce and greater than ½ the previous difference and, if so, atstep 108 calls and validates the weight as the median of the currentpeak, valley pair, and exits. Otherwise, at step 110 microprocessor 30increments counter n, at step 112 tests to determine if n is less thanpredetermined value N. If so microprocessor 30 returns to step 80 toidentify the next peak. Note that now the saved valley used at step 84will be the value saved at step 100.

[0034] If counter n is not less than N than at step 114 microprocessor30 reports an error and goes to an error routine to make a furthereffort to determine the mailpiece weight as will be described furtherbelow with regard to FIGS. 5 and 6. Preferably n is approximately 10.

[0035] Failure of signal S to converge to a value of less than {fraction(1/10)} ounce within N cycles is typically because of the presence ofground vibration. FIG. 4 shows a resulting output signal S′(t) which isthe sum of the normal system response Aexp (−αt) sin (ωt) and groundvibration, which is assumed to have the form Dsin (φt). It is believed,as shown in FIG. 4, the resulting signal S′(t)=Aexp(−αt)sin(ωt)+Dsin(φt) will be periodic even though the amplitude and range of thesignal will vary. Therefore, it is believed that the average of themedians between the resulting peaks and valleys of the signal, M (Pn,Vn), M (Pn+1,Vn), M (Pn+1,Vn+1) . . . , shown in FIG. 4, will vary aboutthe weight W of the mailpiece so that an average over a number of cycleswill give a reasonable estimate of weight W.

[0036]FIG. 5 shows a flow diagram for the operation of themicroprocessor 30 in carrying out the algorithm described above withrespect to FIG. 4. At step 120 microprocessor 30 sums the previous 2Nmedians. Note that the value of the 2N is used because counter n is onlyincremented for every other peak valley pair. Then at step 122microprocessor 30 estimates the weight of the mail piece to be the sumof the medians divided by 2N, and at step 124 calls and validates theweight, and then exits.

[0037] While in the preferred embodiment described with regard to FIGS.4 and 5 all of the 2N medians determined are averaged, in otherembodiments, having different scale systems, it may be found that alesser number of the medians are sufficient to determine a weight withsufficient accuracy. A person skilled in the art can determine if thisis the case through simple experimentation.

[0038] Those skilled in the art will recognize that, in general, asignificant majority of mailpieces require only the minimal postage,i.e., are less than the first weight break. Postage metering system 10takes advantage of this in accordance with the present invention bymaking an early determination of weights less than the first weightbreak as described above and by modifying the accounting for postageexpended by postage meter 16 as is described below with regard to FIG.6.

[0039] In FIG. 6 at step 130 postage meter 16 waits for the presence ofa mailpiece on platform 22. When a mailpiece arrives on platform 22, atstep 132, meter 16 debits vault 17 for the minimum postage amount, andat step 144 forms a corresponding indicium. Then at step 136 meter 16waits for microprocessor 30 to send the postage amount. At step 140meter 16 determines if the postage amount is the minimum amount, and ifso, at step 142 franks the mailpiece and exits. Otherwise, at step 148meter 16 computes any additional postage needed, at step 150 clears theindicium and forms an appropriate new indicium, and at step 152 debitsvault 17 for any additional postage, and goes to step 142 to frank themailpiece with the new indicium. Note that debiting of vault 17 in asecure manner and franking of mailpieces so that postage expended isproperly accounted for is well known to those skilled in the art andneed not be described further here for understanding of the presentinvention.

[0040] The embodiments described above and illustrated in the attacheddrawings have been given by way of example and illustration only. Fromthe teachings of the present application those skilled in the art willreadily recognize numerous other embodiments in accordance with thesubject invention. Particularly other modifications of various indiciaprinted with different geometries will be apparent. Accordingly,limitations on the subject invention are to be found only in the claimsset forth below.

What is claimed is:
 1. A system for determining a weight for an item,comprising: a) a scale system for generating a digital output signal,said scale system comprising: a1) a support for supporting said item;and a2) a transducer for generating said digital output signal, saidsignal being representative of an instantaneous response of saidsupport; and b) a data processing system for, in response to saiddigital output signal: b1) detecting presence of said item on saidsupport; then b2) determining if a next peak to valley difference insaid digital output signal is less then a predetermined value; and, ifso b3) determining said weight to be equal to a median of saiddifference and exiting; otherwise b4) returning to step b2.
 2. A systemas described in claim 1 where said peaks are identified by determiningwhen a first derivative of said digital output signal changes frompositive to negative, and said valleys are identified by determiningwhen said first derivative changes from negative to positive.
 3. Asystem as described in claim 1 where steps b2 through b4 are repeated apredetermined number of times and thereafter said data processing systementers an error condition state.
 4. A system as described in claim 1where said median is identified by determining when a second derivativeof said digital output signal changes from positive to negative.
 5. Asystem as described in claim 1 where said weight is determined only ifsaid median is less than one-half of an immediately previous median. 6.A system for determining a weight for an item, comprising: a) a scalesystem for generating a digital output signal, said scale systemcomprising: a1) a support for supporting said item; and a2) a transducerfor generating said digital output signal, said signal beingrepresentative of an instantaneous response of said support; and b) adata processing system for, in response to said digital output signal:b1) detecting presence of said item on said support; then b2)determining if a next peak to valley difference in said digital outputsignal is less then a predetermined value; and, if so b3) determiningsaid weight to be equal to a median of said difference and exiting;otherwise b4) returning to step b2 a predetermined number of times; thenb5) determining said weight to be an average of said predeterminednumber, or a lesser sufficient number, of previous medians, and exiting.7. A system as described in claim 6 where said peaks are identified bydetermining when a first derivative of said digital output signalchanges from positive to negative, and said valleys are identified bydetermining when said first derivative changes from negative topositive.
 8. A system for determining a weight for an item, comprising:a) a scale system for generating a digital output signal, said scalesystem comprising: a1) a support for supporting said item; and a2) atransducer for generating said digital output signal, said signal beingrepresentative of an instantaneous response of said support; and b) adata processing system for, in response to said digital output signal:b1) detecting presence of said item on said support; then b2)determining if a next peak to valley difference in said digital outputsignal is less then a predetermined value; and, if so b3) determiningsaid weight to be equal to a median of said difference and exiting;otherwise b4) returning to step b2 a predetermined number of times; thenb5) determining said weight to be an average of said predeterminednumber, or a lesser sufficient number, of previous medians, and exiting.9. A system for determining a weight for an item with at leastsufficient accuracy to assure that said weight is within one of aplurality of ranges, said ranges being bounded by break weights, saidsystem comprising: a) a critically damped or overdamped scale system forgenerating a digital output signal, said scale system comprising: a1) asupport for supporting said item; and a2) a transducer for generatingsaid digital output signal, said signal being representative of aninstantaneous response of said support; and b) a data processing systemfor, in response to said digital output signal: b1) detecting presenceof said item on said support; then b2) determining if a first peak insaid digital output signal is less than a lowest of said break weightsand, if so, determining said weight to be in a lowest of said ranges;otherwise b3) determining if a next peak to valley difference in saiddigital output signal is less then a predetermined value; and, if so b4)determining said weight to be equal to a median of said difference andexiting; otherwise b5) returning to step b3.
 10. A system as describedin claim 9 where said predetermined value is a predetermined fraction ofthe smallest of said ranges.
 11. A system as described in claim 10 wheresaid predetermined fraction is approximately one-tenth.
 12. A system asdescribed in claim 9 where said peaks are identified by determining whena first derivative of said digital output signal changes from positiveto negative, and said valleys are identified by determining when saidfirst derivative changes from negative to positive.
 13. A system asdescribed in claim 9 where said median is identified by determining whena second derivative of said digital output signal changes from positiveto negative.
 14. A system as described in claim 9 where said weight isdetermined in step b4 only if said median is less than one-half of animmediately previous median.
 15. A system as described in claim 9 wheresaid data processing system returns to step b3 a predetermined number oftimes and then determines said weight to be an average of saidpredetermined number, or a lesser sufficient number, of previousmedians, and exits.
 16. A system as described in claim 9 where saiditems are mailpieces and postage for said mailpieces is determined bysaid ranges.
 17. A system as described in claim 16 further comprising apostage metering system responsive to said data predestining system forfranking said mailpieces, said postage meter responding to detection ofsaid mailpiece on said support to debit a vault for a minimum postageamount corresponding to said lowest range and then later debiting saidvault for an additional postage amount only if said first peak isgreater than said lowest break weight.
 18. A method for processing anoutput signal, generated by a scale system to determine a weight for anitem on said scale system, said method comprising the steps of: a)detecting presence of said item on said scale system; then b)determining if a next peak to valley difference in said digital outputsignal is less then a predetermined value; and, if so c) determiningsaid weight to be equal to a median of said difference and exiting;otherwise d) returning to step b.
 19. A method as described in claim 18where said peaks are identified by determining when a first derivativeof said digital output signal changes from positive to negative, andsaid valleys are identified by determining when said first derivativechanges from negative to positive.
 20. A system as described in claim 18where said weight is determined only if said median is less thanone-half of an immediately previous median.
 21. A method for processingan output signal generated by a scale system to determine a weight foran item on said scale system, said method comprising the steps of: a)detecting presence of said item on said scale system; then b)determining if a next peak to valley difference in said digital outputsignal is less then a predetermined value; and, if so c) determiningsaid weight to be equal to a median of said difference and exiting;otherwise d) returning to step b a predetermined number of times; thene) determining said weight to be an average of said predeterminednumber, or a lesser sufficient number, of previous medians.
 22. A methodfor processing an output signal generated by a critically damped oroverdamped scale system to determine a weight for an item on said scalesystem, said method comprising the steps of: a) detecting presence ofsaid item on said scale system; then b) determining if a first peak insaid digital output signal is less than a lowest of said break weightsand, if so, determining said weight to be in a lowest of said ranges;otherwise c) determining if a next peak to valley difference in saiddigital output signal is less then a predetermined value; and, if so d)determining said weight to be equal to a median of said difference andexiting; otherwise e) returning to step c.
 23. A method as described inclaim 22 where said predetermined value is a predetermined fraction ofthe smallest of said ranges.
 24. A method as described in claim 23 wheresaid predetermined fraction is approximately one-tenth.
 25. A method asdescribed in claim 22 where said peaks are identified by determiningwhen a first derivative of said digital output signal changes frompositive to negative, and said valleys are identified by determiningwhen said first derivative changes from negative to positive.
 26. Amethod as described in claim 22 where said median is identified bydetermining when a first derivative of said digital output signalchanges from positive to negative.
 27. A method as described in claim 22where said weight is determined in step d only if said median is lessthan one-half of an immediately previous median.
 28. A method asdescribed in claim 22 where said data processing system returns to stepb3 a predetermined number of times and then determines said weight to bean average of said predetermined number, or a lesser sufficient number,of previous medians, and exits.
 29. A method as described in claim 22where said items are mailpieces and postage for said mailpieces isdetermined by said ranges.
 30. A method as described in claim 29 furthercomprising a postage metering system responsive to said datapredestining system for franking said mailpieces, said postage meterresponding to detection of said mailpiece on said support to debit avault for a minimum postage amount corresponding to said lowest rangeand then later debiting said vault for an additional postage amount onlyif said first peak is greater than said lowest break weight.